There is described and claimed in applicants' U.S. Pat. No. 4,480,632 thermal insulation suitable for use along a solar radiation incident surface of a solar pond containing a pond liquid and including a plurality of transparent enclosures arranged to be disposed on a surface of a solar pond, at least one layer of insulative beads disposed within those enclosures, the layer of insulative beads defining a plurality of barrier layers separated from each other by insulating volumes defined by the insulating beads, a liquid material of viscosity greater than the viscosity of the pond liquid being arranged to fill the interstices between the plurality of enclosures, the at least one layer of insulative beads defining the barrier layers being formed of a material selected from the following materials: glass, fluoroplastics, acrylics and polycarbonate and being characterized by transmissivity to solar radiation and opacity to thermal infra-red radiation in the wavelength range of 6-20 microns, the volumes defined by the insulative beads being characterized by low thermal conductivity and high transparency to solar radiation.
There is described and claimed in co-pending U.S. patent application No. 541,119 filed Oct. 12, 1983, solar radiation transmissive insulation apparatus comprising an array of adjacent cells having a geometrical configuration which limits free convection therethrough, the array being generally transparent to solar visible and infra-red radiation and generally opaque to thermal infra-red radiation and a solar pond employing such insulation.